Durability Assessment of Engineered Geopolymer Composites under Freeze–Thaw Conditions

This research examines the long-term durability characteristics of engineered geopolymer composites (EGC) and geopolymer pastes (GPPs) made from basic oxygen steel (BOS) slag, fly ash (FA), and iron ore tailings (IOT), by subjecting them to freeze–thaw (F-T) resistance, drying shrinkage, and water absorption tests. The proposed raw materials are eco-friendly alternatives to cementitious binders and fine aggregates. The proposed durability properties were studied to evaluate the performance of (BOS:FA:IOT) based EGC and (FA:BOS) based GPP mixes. The results showed that the EGC mixes exhibited higher resistance to F-T cycles, minimal weight loss, and enhanced relative dynamic modulus of elasticity compared with the GPP samples. The EGC mixes exhibited strong F-T resistance, with minimal weight loss (<2%) and over 90% relative dynamic modulus of elasticity (Rd) post 85 F-T cycles, indicating their potential in frozen environmental conditions. Additionally, the EGC mixes with higher amounts of BOS slag and IOT exhibited lower shrinkage values during drying (up to 26.4% reduction) and water absorption (up to 21.3% reduction), indicating reduced water permeability. The incorporation of IOT as a partial substitute for conventional fine aggregate in the EGC mixes was also analyzed, and a direct correlation was established between the durability characteristics and the addition of BOS slag and IOT in the geopolymer matrix. The addition of BOS slag and IOT in the proposed EGC resulted in significant improvements in compressive strength (CS) at an optimum replacement level of 40% and 35%, respectively. The pozzolanicity of BOS slag facilitated the formation of calcium silicate hydrates and calcium aluminosilicate hydrates during the geopolymerization process, leading to improved strength. Nonetheless, increased water absorption and lack of IOT increased the permeability nature of GPP, thereby reducing the residual compressive strength and resistance to the freeze–thaw environment. Microstructural analysis using scanning electron microscopy and energy dispersive spectroscopy technique confirmed the absence of toxic elements in the proposed EGC and GPP samples. The morphological aspects obtained reveal the impact of frost attacks on the matrix microstructure, indicating notable variations in the compressive strength, drying shrinkage, and water absorption characteristics. Overall, this study provides valuable insights into the durability characteristics of the proposed EGC and GPP mixes and their potential as sustainable construction and building materials.